The broad objective of the proposed study is to increase our understanding of hospital-based interventions to improve care. The current research is aimed at expanding the paucity of information about methods to increase the utilization that can improve the quality of care, and, particularly, the use of beta- blockers, which have marked variation in usage across the country. Our specific aims will be: to identify the hospital characteristics associated with the change in the use of beta-blockers over a three-year study period (1995-7) and to identify the hospital-based quality improvement interventions that are associated with a marked increase in the use of beta-blockers during the study period. The prescription of beta-blockers for patients after an acute myocardial infarction (AMI) represents an ideal opportunity to study methods of improving quality of care. During the last two decades, beta-blockers have been shown to reduce cardiovascular morbidity and mortality for survivors after AMI. The primary hypothesis of this study is that quality improvement strategies, not hospital characteristics themselves, are strongly associated with marked improvement in the use of beta-blockers at discharge, i.e., the hospitals that improve will not be a specific size or type. Instead, we hypothesize that marked improvement is most strongly associated with a comprehensive intervention strategy that includes the combination of explicit institutional endorsement of standards (e.g., critical pathways, standing orders), the monitoring and feedback of performance, and the clear designation of persons or teams with responsibility for change. To accomplish our aims, we propose a retrospective cohort study and nested case-control to identify hospital-based interventions that are associated with substantial improvements in the use of beta-blockers for survivors of an AMI. We will supplement data from the National Registry of Myocardial Infarction, a national registry of detailed patient information that has more than 600,000 hospitalizations in more than 1,500 hospitals, with information from interviews of QI managers and physicians at 300 hospitals with varying levels of performance. This latter part of the study will be enhanced through the additional partnership of Qualidigm (formerly the Connecticut Peer Review Organization) which will direct the collection of information from the hospitals, and which can provide, through Peer Review statutes, confidentiality for the data.